It is well known that aromatic primary amine color developing agents oxidized by exposed silver halide as an oxidizing agent react with couplers to form dyes such as indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine and the like, whereby a dye image can be formed.
Couplers useful for forming a magenta dye image include 5-pyrazolone, cyanoacetophenone, indazolone, pyrazolobenzimidazole.
Most of the couplers which have been conventionally used as magenta dye image forming couplers and which have been extensively studied include the 5-pyrazolone compounds. However, it is known that in dyes formed from 5-pyrazolone couplers, there exists an unnecessary absorption having a yellow component in the vicinity of 430 nm and color turbidity is caused thereby.
A pyrazolobenzimidazole skeleton described in U.K. Patent 1,047,612, an indazolone skeleton described in U.S. Patent 3,770,447 and a pyrazolo[5,1-c]-1,2,4-triazole skeleton described in U.S. Pat. No. 3,725,067 have been proposed as magenta dye image forming skeletons which reduce the yellow component.
The present inventors have previously developed pyrazoloazole magenta couplers such as imidazo[1,2-b]pyrazoles, pyrazolo[1,5-b][1,2,4]triazoles, pyrazolo-[1,5-d]tetrazoles, pyrazolo[1,5-d]benzimidazoles and pyrazolopyrazoles as magenta couplers which have good color formability and exhibit less unnecessary absorption of yellow color. However, it has been found that azomethine dyes formed from such pyrazoloazole couplers have relatively poor fastness to light, or heat-moisture and are not sufficiently prevented from being faded when conventional dye image stabilizers (e.g., alkyl-substituted hydroquinones) are used.
Attempts to solve the problems referred to hereinabove have been made by adding various compounds. For example, there are known methods wherein hindered amine derivatives are added, described in JP-A-62-178241 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-62-278551, JP-A-63-231340, JP-A-61-4045, JP-A-62-92945 and European Patents 242211 and 218266 and methods wherein hindered piperidine derivatives having phenolic hydroxyl group in the molecular structure are added, described in JP-B-57-20617 (the term "JP-B" as used herein means an examined Japanese patent publication"), JP-A-58-114036, JP-A-59-53846, JP-A-59-78344, JP-A-59-109052, JP-A-59-113441, JP-A-59-116747, JP-A-59-119351 and JP-A-59-133543. However, these compounds do not have a satisfactory effect of preventing azomethine dyes formed from the pyrazoloazole couplers from being faded, and some compounds have an adverse effect on photographic characteristics.
Methods wherein alkoxybenzene derivatives are added are described in JP-A-60-262159, JP-A-59-125732, JP-A-61-282245, JP-A-62-244045, JP-A-62-244046, JP-A-62-273531, JP-A-61-158330, JP-A-63-95439, JP-A-63-95448, JP-A-63-95450 and JP-A-63-284548. These compounds have an effect of improving fastness to light in the high density region of dyes formed by the couplers, but do not have a sufficient effect in the low density region of dyes when the amount of exposure is small.
Further, methods wherein four or more different compounds are used in combination have been proposed to give a synergistic effect, thus improving the problem with respect to fading by light. For example, methods wherein hindered amine derivatives are used in combination with different compounds (e.g., hydroquinone derivatives, alkoxybenzene derivatives, etc.) are disclosed in JP-A-62-183459, JP-A-62-180367, JP-A-62-246053, JP-A-62-96944, JP-A-62-253168, European Patents 218266 and 242211. However, these methods have neither a remarkable synergistic effect nor a sufficient effect of improving fastness to light in the region of low density.
Generally, couplers and fading inhibitors are dissolved in high-boiling organic solvents in order to use them. The color formability of the couplers, the hue of the formed colors and the fastness to light, heat and moisture are greatly affected by the high-boiling organic solvents. Hence, the development of novel high-boiling organic solvents and methods for using them have been examined. For example, JP-A-62-180367, JP-A-62-246053 and European Patent 242211 disclose the use of phthalic ester type high-boiling organic solvents, and European Patent 218266 discloses the use of phosphoric ester type high-boiling organic solvents. In the phthalic ester type high-boiling organic solvents, however, foot cutting on the long wave side of the absorption wave of formed dyes is not good, and color reproducibility is not sufficiently improved.
Accordingly, it would be useful to develop a technique which does not have an adverse effect on photographic characteristics, gives good color-reproducibility, can inhibit fading by light, particularly requires a lower amount of exposure and hence can inhibit fading by light in the region of low color density.